The present invention relates to an improved mode switch.
A typical conventional mode switch is shown in FIGS. 25, 26 and 27. The conventional mode switch includes arc stationary contacts 102 with respective predetermined lengths exposed and formed in the form of plural concentric circles on the upper surface of a base 101, and a single comb-like movable contact spring piece (generally called brush) 104 attached on the lower surface of a disc rotor 103 and having plural contact spring pieces arranged in parallel with one ends acting as contacts. The center shaft 105 on the base 101 is rotatably fitted to the center hole 106 in the rotor 103. The contacts of the movable contact spring piece 104 sliding over the upper surface of the base 101 in a contact state are slidably and sequentially contacted to the stationary contacts 102 (or are turned ON) by rotating the rotor 103. When the contacts of the movable contact spring pieces 104 are opened from the stationary contacts 102 (or come to the positions where the stationary contacts 102 are not exposed), the mode switch is turned OFF.
Generally, in order to rotatably mount the rotor 103 to the base 101 without dropping, the mounting cover 111 for covering the whole surface of the rotor 103 is attached to the base 101 by inserting the engaging protrusions 112 of the base 101 into the engaging holes 111a in the right and left side plates.
Since the movable contact spring piece 104 always slides under pressure on the inner surface of the base 101 (on the insulating surface and stationary contacts), together with the rotor 103 rotated, grease is always applied on the movable contact spring piece 104, so that the rotation of the rotor 103, that is, the sliding of the movable contact spring piece 104 although always in contact with the inner surface of the base is always maintained smooth.
A loss of such smoothness causes erroneous signal reception or noise mixture.
However, the use of grease leads to the following drawbacks:
(1) A grease film formed on the contact surface of a contact may interfere with good electrical conduction of the contact. PA1 (2) Particles or dusts caused by the friction during the sliding operation contaminate the grease and degrades the lubrication or conduction.
The grease may solidify or be degraded during a long service period, thus deteriorating the lubrication, conduction, or the like.
As described above, since the metal movable contact spring piece 104 directly slides over the metal stationary contacts 102 under pressure, metal particles produced in the sliding and polishing operation tend to cause a contact failure. Thus, variations in contact state at different portions result in noises. For that reason, a mode switch that does not use any grease and does not have its contacts slidably contacted to each other has been long desired.
In the mode switch, the stationary contacts 102 on the base 101 must be always juxtaposed with the contacts of the movable contact spring piece 104 on the lower surface of the rotor 103 with high precision with no variations in mode switches. In order to realize such requirements, the fitting accuracy must be set between the center shaft 105 of the base 101 and the center hole 106 of the rotor 103 must be fit together as accurately as possible and set a gap between the outer diameter of the shaft and the inner diameter of the shaft hole as small as possible. Since the rotor must be lightly rotated by a very small rotational force, the shaft is loosely fitted to the gap which allows sufficient mobility. The base and the rotor are a molded pieces made of general-purpose plastic (not special plastic for expense precision devices). Hence, variations in these molded products may cause irregular rotation of the rotor.
Moreover, in the conventional mode switch, in order to prevent the irregular rotation, the resilient recovery force of the movable contact spring piece presses the upper surface of the rotor against the lower surface of a mounting cover which covers the whole surface of the rotor and which prevents the rotor from being dropped off, thus stopping the moving of the rotor. However, the mounting covers, which are formed through a sheet metal shaping process under pressure, varies in their dimensions means for attaching the mounting cover to the base, for example, the engagement between the mounting cover engaging hole and the engaging protrusion on the base, requires high precision in their dimensions. Hence, variations in spacing in each switch make it difficult to improve the switching performance.
In the conventional mode switch, the rotor must be attached with a different mounting cover. This makes it difficult to reduce the number of constituent components for a mode switch the fabrication steps and the manufacturing costs, and also to improve the productivity.